This invention relates generally to an electrophotographic printing machine, and more particularly concerns a color discrimination system for automatically sensing the position of colored or encoded portions on an original document being copied, and for controlling erase and development means to produce an output color copy.
Hereinbefore, multicolor copying was achieved by using a multicolor electrophotographic printing machine. In the process of electrophotographic printing, a photoconductive surface is charged to a substantially uniform potential. The photoconductive surface is image-wise exposed to record an electrostatic latent image corresponding to the informational areas of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document. Thereafter, a developer material is transported into contact with the electrostatic latent image. Toner particles are attracted from the carrier granules of the developer material onto the latent image. The resultant toner powder image is then transferred from the photoconductive surface to a copy sheet and permanently affixed thereto. The foregoing generally describes a typical black and white electrophotographic printing machine. With the advent of multicolor electrophotographic printing, the process is repeated for three or four cycles with the charged photoconductive surface being exposed to a filtered light image. The resultant electrostatic latent image is then developed with toner particles corresponding in color to the subtractive primary of the filtered light image. For example, when a red filter is employed, the electrostatic latent image is developed with cyan toner particles. The cyan toner powder image is then transferred to the copy sheet. The foregoing process is repeated for a green filtered light image which is developed with magenta toner particles and a blue filtered light image which is developed with yellow toner particles. Each differently colored toner powdered image is sequentially transferred to the copy sheet in superimposed registration with the powder image previously transferred thereto. In this way, three toner powder images are transferred sequentially to the copy sheet. After the tone powder images have been transferred to the copy sheet, they are permanently fused thereto. Thus, color electrophotographic machines previously employed require three passes to produce a multicolor copy. A typical electrophotographic printing machine employing the foregoing process is manufactured by the Xerox Corporation under the model name Xerox 1005.
These prior art machines are referred to as full process color machines and are capable of copying full color originals. The machines are relatively costly and operate at reduced speeds, relative to black and white copiers.
There exists significant applications wherein original documents to be copied have portions of the text which are of a distinctive color designed to distinguish over the remainder of the information on the document. For example, an original document may have one portion wherein the indicia is red while the remainder is monochrome. The red portion is often referred to as the "highlighted" portion of the document. While the aforementioned multicolor copying machines can produce a faithful color copy of such a color original, it would be desirable to accomplish the same end by a means less expensive and faster in operation.
Also known in the prior art are copiers capable of image editing and so called "push button color". Typical of such copiers is the Canon NP-3525. A key pad on the machine is used to select the coordinates of the region of the copy to be reproduced as a highlight color. A platen, upon which an original document is positioned, has a coordinate grid thereon. This enables the operator to select the coordinates of the copy to be reproduced in a highlight color. These coordinates are keyed into the control system of the printing machine by the operator selecting the appropriate keys of the key pad. The control system actuates selected lamps of a light source at the appropriate time in the cycle to erase the portion of the electrostatic latent image corresponding to the region of the copy to be reproduced in a highlight color. The remaining portion of the electrostatic latent image is developed with black toner. On a second pass image scan, the selectable erase lamps discharge the black portion of the electrostatic image and the remaining portion is developed by a second highlight color developer. With this type of system, it is possible to copy an original document having one or more desirable colored portions. However, this requires an operator input. For example, if an original document has a discrete area with a red text thereon, and it is desired to produce an output copy faithful to the original, the operator must select the coordination of the original, enter them into the control system and select the color, in this case red.
It would be a desirable feature for a printing machine to have the capability of automatically identifying an original which has both black and color areas and of producing output copies reproducing these areas. It would also be desirable to create output copies of original documents wherein the contents and/or color of the original document is altered from its original state. Deletion of certain portions of an original document might be one example while a highlighting of certain portions of a document in a highlight color different than that identified in the original would be another. This second feature may be referred to as an "editing" function. Both features are realized, according to the present invention, by scanning the document to be copied, either prior to the initiation of a copy mode (e.g. in a prescan mode) or, preferably, at the same time the original document is being exposed. The light image is projected through a lens onto a low resolution, solid state photosensor array which incorporates appropriate color filters. The array can be adapted to either detect any color other than black or can recognize one of a plurality of colors. The array generates electrical output signals representing the sensed original image. The array output signals are digitized within a control system. An appropriate algorithm is used to establish the position (coordinates) of the colored portions of the original and to temporarily store the signals representing these coordinates. The control system, during appropriate times of the operation cycle, generates signals causing erase of portions of a latent image formed on the photoconductor and/or causes the remaining image to be developed with a developer material of the appropriate color. The final output copies are made using multiple imaging and development passes.
The following U.S. patents have been identified as disclosing relevant subject matter:
U.S. Pat. No. 4,368,484 to Stemme et al discloses a device for color scanning with a CCD array to reproduce photographic positives or negatives as video images. The device also includes a shift register unit and a clock pulse generator. Individual output channels for each of the three primary colors are connected to a gamma-balancing stage to effect contrast corrections.
U.S. Pat. No. 4,642,679 to Nagano discloses a color image reading apparatus in which a CCD is provided for detecting images under green, red, and blue light. Voltage produced from the CCD is applied to a sample/hold circuit which then produces a voltage V.sub.o. This second voltage is applied to a subtraction circuit comprising a register, buffer, D/A converter multiplier and three memories.
Japanese Laid Open (Kokai) Publication 62-161260 discloses an image-forming system which uses an optical system including photoelectric devices to identify color areas manually highlighted on an original.
Xerox Disclosure Journal Vol. 11, Number 5, October 1986, p. 253 discloses use of a double filter over a CCD array which, in conjunction with an electric circuit, identifies areas of an original highlighted with a yellow pen.
U.K. publication 6B 2,066,610 employs a CCD array to identify areas of an original which have been marked with a particular color.
In accordance with one aspect of the present invention, there is provided a color printing machine for printing color output copies of a color document, the machine including:
a xerographic imaging system comprising a photoconductor member, means for charging the surface of said member, scanning optical means for forming successive latent electrostatic images of said original on the surface of said member, means for erasing selected portions of said latent image, means for developing the latent image in at least two colors, means for transferring said developed image to a copy sheet and means for fusing said transferred image, said imaging system further comprising:
sensing means for discriminating between colored areas of said original document and for generating electrical signals representative of said colored areas, control means adapted to digitize and store said sensing means output signals, said control means further adapted to operate said erase means so as to erase areas of at least a first and second latent image, and to operate said developer means so as to develop the remaining latent image, following said erase operation, with a color toner appropriate to the color of the non-erased image.